Pillow Cover / Box Cushion Fabric Calculator
Calculate fabric yardage for a flat pillow cover or a box cushion with side boxing.
Reviewed by the ToolNestr Editorial Team — July 2026
How pillow and cushion fabric is calculated
A flat pillow cover needs two panels (front and back), each the finished width and length plus seam allowance on every side, so total fabric is simply twice that panel's area, laid out to fit your fabric's width. A box cushion needs the same two panels for top and bottom, plus a boxing strip that wraps around the sides — this strip's length equals the cushion's perimeter (2 × width + 2 × length) and its width equals the cushion height plus seam allowance.
The calculator adds these pieces together, accounting for how many fit per row across your fabric's width, to give a total yardage figure covering every panel needed for the cover.
This follows standard home-decor sewing construction for flat pillow covers and boxed cushions with a separate boxing strip.
Worked example
A 20 × 20 inch box cushion, 4 inches deep, 0.5-inch seam allowance, 54-inch fabric.
Real-world context
Outdoor patio furniture cushions are one of the most common box-cushion projects, since replacement covers for weathered factory cushions are often expensive to buy pre-made but straightforward to sew once fabric quantity is known — getting the boxing strip length right the first time avoids piecing together short offcuts around a cushion's full perimeter.
Matching a set of throw pillows to a room's decor is the classic flat-pillow-cover use case, and calculating combined yardage for several pillows at once (rather than estimating per pillow) usually finds a more efficient fabric layout and avoids buying in awkward partial-yard increments repeatedly.
Common misconceptions
"A box cushion just needs a bit more fabric than a flat pillow of the same size." Often significantly more. The boxing strip alone can equal or exceed the fabric used for both flat panels combined, especially on a deep cushion, so box cushions frequently need noticeably more total fabric than a flat cover of the same footprint.
"Seam allowance only matters on the outer edges." It applies everywhere fabric pieces join. The boxing strip needs seam allowance on both long edges (where it joins the top and bottom panels), not just where it's cut to length.
Related tools
Frequently asked questions
What is a boxing strip?
A boxing strip (or gusset) is the fabric band sewn around the sides of a box cushion, giving it depth — a flat pillow cover has no boxing strip since front and back panels are sewn directly together at the edge.
How much seam allowance should I add?
A standard 0.5-inch seam allowance is common for pillow and cushion covers; enter your finished size and the calculator adds the seam allowance to all sides automatically.
Do I need extra fabric for a zipper?
A small additional allowance (often 1-2 inches) on the panel with the zipper opening is common to accommodate the zipper facing and overlap — add this to your seam allowance input if your design includes a zipper closure.
How is boxing strip length calculated for an odd-shaped cushion?
This calculator assumes a rectangular cushion, where boxing strip length equals the perimeter (2 × length + 2 × width). For a round or custom-shaped cushion, measure the actual perimeter directly and use it in place of the calculated rectangular perimeter.